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Changing telnet ports: A security solution?

Changing telnet ports is not a means by which to make your AS/400 servers secure. To manage the TCP/IP settings on the System i, you use the STRTCPSVR command. But you need to know how to manage these settings first.

My company has two iSeries servers installed. i would like to know how tochange the Telnet port to block outside acccess to the servers, (without interrupting the iSeries access and navigator to connect using the new port no.) And also, how do I restart the Telnet server?
If you think that changing the telnet port will provide an additional layer of security, you're wrong. That's "security by obscurity" and the new port is very easily discovered. If you want to prevent someone from using telnet then you'll have to write a telnet exit program to prevent it's use. You manage all TCP/IP servers on the system using the STRTCPSVR command. From the questions you are asking, you are new to security and the System i – before you make any changes, I suggest you read up on the TCP/IP concepts on System i or many things are going to start to break.

Editor's Note: You may want to start by reading the iSeries Resource Guide for Newbies. Then read Chapter 2 of the IBM Redbook V5 TCP/IP Applications on the IBM eServer iSeries Server.

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